The present invention relates generally to the cloning, identification, and expression of multiple repeat sequences of the CA125 gene in vitro and, more specifically, to the use of recombinant CA125 with epitope binding sites for diagnostic and therapeutic purposes.
CA125 is an antigenic determinant located on the surface of ovarian carcinoma cells with essentially no expression in normal adult ovarian tissue. Elevated in the sera of patients with ovarian adenocarcinoma, CA125 has played a critical role for more than 15 years in the management of these patients relative to their response to therapy and also as an indicator of recurrent disease.
It is well established that CA125 is not uniquely expressed in ovarian carcinoma, but is also found in both normal secretory tissues and other carcinomas (i.e., pancreas, liver, colon) [Hardardottir H et al., Distribution of CA125 in embryonic tissue and adult derivatives of the fetal periderm, Am J Obstet. Gynecol. 163;6(1):1925-1931 (1990); Zurawski V R et al., Tissue distribution and characteristics of the CA125 antigen, Cancer Rev. 11-12:102-108 (1988); and O'Brien T J et al., CA125 antigen in human amniotic fluid and fetal membranes, Am J Obstet Gynecol. 155:50-55, (1986); Nap M et al., Immunohistochemical characterization of 22 monoclonal antibodies against the CA125 antigen: 2nd report from the ISOBM TD-1 workshop, Tumor Biology 17:325-332 (1996)]. Notwithstanding, CA125 correlates directly with the disease status of affected patients (i.e., progression, regression, and no change), and has become the “gold standard” for monitoring patients with ovarian carcinoma [Bast R C et al, A radioimmunoassay using a monoclonal antibody to monitor the course of epithelial ovarian cancer, N Engl J Med. 309:883-887 (1983); and Bon G C et al., Serum tumor marker immunoassays in gynecologic oncology: Establishment of reference values, Am J Obstet. Gynecol. 174:107-114 (1996)]. CA125 is especially useful in post-menopausal patients where endometrial tissue has become atrophic and, as a result, is not a major source of normal circulating CA125.
During the mid 1980's, the inventor of the present invention and others developed M11, a monoclonal antibody to CA125. M11 binds to a dominant epitope on the repeat structure of the CA125 molecule [O'Brien T J et al., New monoclonal antibodies identify the glycoprotein carrying the CA125 epitope, Am J Obstet Gynecol 165:1857-64(1991)]. More recently, the inventor and others developed a purification and stabilization scheme for CA125, which allows for the accumulation of highly purified high molecular weight CA125 [O'Brien T J et al., More than 15 years of CA125: What is known about the antigen, its structure and its function, Int J Biological Markers 13(4): 188-195 (1998)].
Considerable progress has been made over the years to further characterize the CA125 molecule, its structure and its function. The CA125 molecule is a high molecular weight glycoprotein with a predominance of O-linked sugar side chains. The native molecule exists as a very large complex (˜2-5 million daltons). The complex appears to be composed of an epitope containing CA125 molecule and binding proteins which carry no CA125 epitopes. The CA125 molecule is heterogenous in both size and charge, most likely due to continuous deglycosylation of the side chains during its life-span in bodily fluids. The core CA125 subunit is in excess of 200,000 daltons, and retains the capacity to bind both OC125 and M11 class antibodies. While the glycoprotein has been described biochemically and metabolically by the inventor of the present invention and others, no one has yet cloned the CA125 gene, which would provide the basis for understanding its structure and its physiologic role in both normal and malignant tissues.
Despite the advances in detection and quantitation of serum tumor markers like CA125, the majority of ovarian cancer patients are still diagnosed at an advanced stage of the disease—Stage III or IV. Further, the management of patients' responses to treatment and the detection of disease recurrence remain major problems. There, thus, remains a need to significantly improve and standardize current CA125 assay systems. Further, the development of an early indicator of risk of ovarian cancer will provide a useful tool for early diagnosis and improved prognosis.